The invention pertains to a pipe sealing pad having a cylindrical, external sleeve of reinforced rubber material and two end walls which are also made of rubber. The sleeve and the end walls are joined together by heat-vulcanization and define an air-tight compartment which is accessible via a connection comprising a pipe fitting which is attached to one of the two faces. The pipe fitting inside the air-tight compartment is connected to a rubber ring disk which is connected to the inner surface of the end wall in question so as to be hermetically sealed.
Such pipe sealing pads generally have either a purely cylindrical form or a ring shape. With respect to the ring-shaped pipe sealing pads, a cylindrical sleeve into which a purely cylindrical pipe sealing pad can be inserted is generally attached to, or incorporated in, the construction. In addition, there are pipe sealing pads fitted with connecting pipeing between both end walls of the sealing pad. Such pipe sealing pads are frequently designated `testing pads`. These piipe sealing devices may be used for sealing off piping quickly, especially if the pipe has been damaged or has sprung a leak. The piping can be blocked off quickly, reliably and eminently practically above the section to be tested or repaired. In this way damage which could ensue because of the defective piping--damage such as pollution due to the discharge or spreading of waste water or other liquids which would contaminate ground water--can be reduced to a minimum.
The pipe sealing pad of the type named above, described in the U.S. Pat. No. 4,377,184 has cup shaped end walls with the circular, cylindrical wall sections being turned inwardly, and vulcanized to the inner surface of the sleeve, tapering like an arrow to the free edge. The sleeve is reinforced along the axis. With respect to this type of seal, however, it is a disadvantage that it cannot be vulcanized under heat in one single operation. Rather, the sleeve must first be connected to one of the end walls, whereupon in the second process of vulcanization it is connected to the second end wall, which for this purpose has an innter supporting component in the internal compartment.
In addition, the connection between the air attachment and the pertinent end wall is a weak point. This becomes evident when the sealing pad is frequently used; i.e., during inflation, the pipe sealing pad blows up just like a cask. The sleeve assumes the greatest diameter in the vicinity of its longitudinal center, and from this position the diameter declines as it progresses towards both faces, while the diameter of the two end walls remains partically unchanged, although they do bulge out convexly. Thus, the material of the pertinent end wall sited near, or attached to, the ring disk is drawn out and away from the pipe fitting. The opening through which the pipe fitting passes, which is a weak point anyway, is enlarged. This expansion in the region of the pipe fitting leads, especially after a number of inflations, to a gradual weakening of the union between the pipe fitting or the ring disk and the section of the end walls to which this is joined. The connection gets progressively weaker and there is a danger that it will start to leak.
This effect is combatted in the already existing pads of the kind described above by reinforcing the sleeve but not the end walls of the sealing pads. In this way the end walls have a greater elasticity than the sleeve which, because it is reinforced, is for all practical purposes incapable of expansion in the direction in which it is reinforced. This type of construction nevertheless poses problems by reason of the fact that if the side walls are made of material of the same strength as the sleeve they expand vigorously when inflated, thereby causing suction forces in the vicinity of the air connection. For this reason the end walls are usually constructed very thick so that they do not pull out of shape. But if this is done the pad is rendered heavy, a lot of material is required, and the connection between the sleeve and the end walls become critical. Indeed, it cannot be satisfactorily resolved on a permanent basis.
With respct to the pipe sealing pads in U.S. Pat. No. 3,459,230, the sleeve and the end walls are, to be sure, constructed in one single vulcanization process, but in their construction an inner, essentially can-shaped supporting frame made of metal is utilized. This supporting frame then remains in the inner compartment. This is a disadvantage. The air connection is attached externally to the one face of the pad, and the connecting ring disk which is joined to the rubber pipe support is vulcanized eccentrically on the outside of one of the end walls. But in this type or model, the ring disk has to perform all of the expansion movements to which the pertinent end wall is subjected during inflation. The expansions which occur during this process cause in time damage to the connection between the ring disk and the face of the pad, especially in view of the fact that by reason of the external arrangement of the ring disk the connection between the ring disk and the end wall is subjected to additional pressure within the compartment. In contrast, the inner pressure when the ring disk is mounted on the inside of the end wall functions as a type of reinforcing of the connection between the ring disk and the end wall of the pad.
Taking as the starting point the pipe sealing pad of the kind described initially, it was the purpose of the invention to avoid the disadvantages of this pipe sealing pad and create a pad which is so constructed in its manufacture during a single vulcanizing process that the connection of the air connection to the relevant end wall of the pad is solid and permanent. The expansion forces which invariably are generated during inflation of the sealing pad are absorbed in such a way that even over time no leaking spot will occur. The end walls can be manufactured as desired, that is, whether reinforced or not, and in whatever thickness desired, although it is preferable to have them as thin as is practicable.